In a previous study, we found, against our expectations that thoracic epidural analgesia significantly inhibits the detrusor muscle during voiding, resulting in clinically relevant post void residuals which required monitoring or transurethral catheterisation 9. Because the study adopted a before-after design, we could not definitively identify the mechanisms responsible for bladder dysfunction. In particular, we could not say whether thoracic epidural analgesia per se or surgery was the cause of bladder dysfunction. Furthermore, it remains which ingredients, whether the local anesthetic, the opioid or both are behind changes in voiding function.